By DAVID STREITFELD

February 5, 2014

For travelers trying to economize, the ability to rent someone’s spare bedroom is a real breakthrough. Cities like New York, London and Paris are easier to visit than they have been in many years.

But for those who actually work in the hotel industry, this business model is bad news: Airbnb and its imitators might eventually put them out of a job.

A new study by researchers at Boston University demonstrates for the first time that as the so-called sharing economy rises, the traditional lodging industry gets squeezed. For every 1 percent increase in the size of the Airbnb market, the researchers found, hotel revenue slips 0.05 percent.

That does not sound like much of a drop. But Airbnb is expanding at a rapid clip. It now offers a half-million rentals around the world. Its chief executive, Brian Chesky, recently tweeted that the company would add 30,000 new rooms in the next two weeks.

The researchers focused on Texas, using publicly available data from Airbnb as well as tax data.

“Our study suggests that lower-tier hotels in dense Airbnb areas should be concerned,” said Georgios Zervas, an assistant professor of marketing at Boston University. “And if Airbnb keeps growing at the same rate, ‘fear’ might be a more accurate word.”

Airbnb, which was founded in San Francisco in 2008, regularly issues studies saying how much it adds to the local economy. Last week, for instance, it reported it had generated $824 million in economic activity in the United Kingdom in one year and supported 11,629 jobs.

Communities, however, look at Airbnb and see diminishing tax revenue, illegal short-term rentals and other problematic issues. Eric Schneiderman, the New York attorney general, issued an investigatory subpoena to Airbnb in October, asking for a list of its hosts in the state and how much revenue they were generating. Airbnb is fighting the request.

Mr. Schneiderman suspects that many rentals in New York are offered by professionals who have multiple units but evade regulation. The Texas study suggested that this phenomenon was probably widespread. More than 100 hosts in Austin have more than three listings available.

Airbnb declined to comment. Mr. Chesky, in a BBC interview, said Airbnb posed only limited competition to traditional hotels. “I’m not going to say there is no overlap, but there is a lot of new activity happening for the very first time,” he said. “It’s not completely zero sum.”

The researchers see a bigger threat, particularly for hotels in the bottom half of the market. At least so far, Airbnb is not much competition for luxury resorts and big-city hotels that cater to business travelers.

“We estimate that Airbnb’s growth has negatively impacted the revenue of lower-tier hotels by about 5 percent over the past two years,” Mr. Zervas wrote in an email. “If it keeps growing at the same rate over the next couple of years and the experience in Texas is representative, we could see an additional 5 percent impact, for a total of 10 percent.”

That might not kill inexpensive motel chains, but it will certainly crimp their business. The sharing economy is rolling out quickly — look at the rise of Uber and its ride-sharing competitors — with little sense of what the consequences are for safety, the economy or employment.

“I’d like to know the total size of the sharing economy and how much positive change it’s bringing in people’s lives,” Mr. Zervas said. “I’d also like to know what policies are needed to encourage such positive change while at the same time curbing bad uses, such as running illegal hotels or hoarding rental apartments and putting them on Airbnb for profit.”